Sub-sector-based codebook feedback for massive MIMO with 2D antenna arrays

Massive MIMO is a promising technology for next generation cellular networks. It differentiates from conventional MIMO systems because of the excessive number of transmit antennas at the base stations. To implement a massive MIMO system with FDD, a practical low-overhead downlink channel training and estimation method is required. We propose a codebook based feedback framework for FDD massive MIMO systems that divides the coverage area into sub-sectors, where each sub-sector is formed by a set of narrow beams that cover a pre-assigned area in azimuth and elevation. A feedback process is then used where the codebook based feedback is limited to the beams covering the sub-sector to which the user device belongs. Our simulation results show that the proposed feedback framework with a large 2D antenna array provides substantial performance improvement compared to existing LTE/LTE-Advanced systems that currently support no more than eight antenna ports.